Through recent studies, smart materials are widely used for various issues related with an active or passive control of structure. These materials may be shape memory alloy, piezoelectric element, electroactive polymer, and etc. These smart materials may be directly attached to the structure, or may be inserted into another material to be used as an actuator.
Roger (Craig A. Rogers, “Active vibration and structural acoustic control of shape memory alloy hybrid composites: Experimental results,” The Journal of the Acoustical Society of America, Vol. 88, No. 6, pp. 2803-2811, 1990) performed an experiment for restricting vibration by preparing a shape memory alloy embedded composite, and applying an additional stress to a structure by actuating the prepared composite. Baz (A. Baz, T. Chen, and J. Ro, “Shape control of NITINOL-reinforced composite beams,” Composites: Part B, Vol. 31, pp. 631-642, 2000) performed an experiment for providing a shape-changeable structure through the use of shape memory alloy embedded composite. Jung (B. S, Jung, M. S. Kim, Y. M. Kim, W. Y. Lee, and S. H. Ahn, “Fabrication of smart air intake structure using Shape Memory Alloy wire embedded composite,” Physica Scripta, accepted, 2010) performed an experiment for preparing shape memory alloy embedded glass fiber composite, and developing various methods in order to improve actuating quantity. Villanueva (A. A. Villanueva, K. B. Joshi, J. B. Blottmanm, and S. Priya, “A bio-inspired shape memory alloy composite (BISMAC) actuator,” Smart Materials and Structure, Vol. 19, pp. 1-17, 2010) performs an experiment for preparing various shapes of actuator through the use of shape memory alloy and room-temperature vulcanizable silicon, and measuring actuation varying based on the shape.
By studying a small-sized robot using the shape memory alloy, Kim (B. K Kim, M. G Lee, Y. P Lee, Y. I Kim and G. H Lee, “An earthworm-like micro robot using shape memory alloy actuator”, Sensors and Actuators A 125 (2006) 429˜437) fabricated an earthworm-like robot capable of moving forward through the use of shape memory alloy, shrinkable tube, and needle for determining a moving direction. Koh (J. S Koh and K. J Cho, “Omegabot: Biominetic Inchworm Robot using SMA Coil Actuator and Smart Composite Microstructures (SCM)”, International Conference on Robotics and Biominetics, Dec. 19-23, 2009, Guilin, China) fabricated an inchworm robot, named ‘Omegabot’, through the use of shape memory alloy and composite prepared by SCM process. Kim (M. S. Kim, W. S. Chu, J. H. Lee, Y. M. Kim, B. S. Jung and S. H. Ahn, “Manufacturing of inchworm robot using Shape Memory Alloy (SMA) embedded composite structure,” International Journal of Precision Engineering and Manufacturing, accepted, 2010) manufactured an inchworm robot capable of moving forward by providing a shape memory alloy embedded glass fiber composite with specially-prepared feet whose frictional force varies according to a moving direction.
Other smart structures may be multi-stable complex structures, and shape memory alloy composites. The multi-stable complex structures may be a bi-stable morphing airfoil proposed by Diaconu (Diaconu, C. G., Weaver, P. M., Mattioni, F., Concepts for morphing airfoil sections using bi-stable laminated composite structures, Thin-Walled Structures 46 (6), pp. 689-701, 2008), and a multi-stable morphing wing proposed by Iannucci (L. Iannucci and A. Fontanazza, Design of Morphing Wing Structures, 3rd SEAS DTC Technical Conference, Edinburgh, 2008). These multi-stable complex structures are maintained in the deformed state without additional energy. However, these multi-stable complex structures are disadvantageous in that they can be deformed only in the designed shape, that is, it is difficult to change the structures to the desired shape. The shape memory alloy composites are most generally known as the smart structure, which have been actively studied by Lagoudas et al. 1994, Kawai et al. 1999, Murasawa et al. 2004, Khalili et al. 2007a, b, Yongsheng and Shuangshuang 2007, Zhou et al. 2004, Dano and Hyer 2003, and etc. These kinds of smart structure can be controlled to be deformed in the desired shape, but it needs additional energy. The aforementioned smart structures are limited only to hard matrix. However, soft smart structures are required to realize a biomimetic technology. Ilievski (Ilievski, F., Mazzeo, A. D., Shepherd, R. F., Chen, X., Whitesides, G. M., Soft robotics for chemists, Angewandte Chemie—International Edition 50 (8), pp. 1890-1895, 2011) proposed a soft robot using soft materials of PDMS and Ecoflex.
Through recent studies, the smart materials are widely used for various problems related with the active or passive control of structure. These materials may be shape memory alloy, piezoelectric element, electroactive polymer, and etc. These smart materials may be directly attached to the structure, or may be inserted into another material to be used as an actuator. However, deformation of the structure using most of the smart material is limited to linear deformation or out-of-plane bending deformation, and the degree of deformation is too low, thereby causing the limited utilization. Also, since the actuator occupies too large space in the entire structure, it is difficult to obtain a small-sized structure.